The spine is formed of superposed vertebrae, from the lumbar vertebrae to the cervical vertebrae, each having an anterior part, which is the vertebral body, and a posterior part, which is the vertebral arch (or neural arch), the anterior and posterior parts enclosing the vertebral foramen. Each vertebral arch is formed by a pair of pedicles and a pair of laminae, and has transverse processes and/or a spinous process (or neural spine) projecting therefrom. The transverse and spinous processes project opposite to the vertebral foramen.
If the spine of a person has abnormal curvature, the vertebrae are abnormally inclined relative to one another. Typically, the lateral edges or the spinous processes of adjacent vertebrae are closer together or further apart than they should be.
As a remedy for this situation different kinds of known devices may be used to straighten the spine.
A first kind of device known in the art is a hook and rod device with hooks that are hooked on the inner surface of the vertebral foramen, and a rod for connecting two or more hooks together. Known examples of hook and rod devices are disclosed, for instance, in the PCT patent application no WO 2005/023126 and in U.S. Pat. No. 4,269,178. However, using hooks may be difficult, especially because their use increases the risk that the physician (or other operative) might contact and potentially damage the spinal cord that extends along the vertebral foramen (which may result in paralysis of the patient).
Another kind of known device is a screw and rod device with screws that are screwed into the vertebrae, and a rod for connecting two or more screws together. A known example of screw and rod device is disclosed, for instance, in European patent no EP 1575433B1. The screws typically are inserted in pairs into the pedicles of a vertebra, on each side of the spinous process, thereby constituting fixing points on the vertebrae for holding the vertebrae. However, in some cases, the pedicles are small or have deteriorated and may be damaged or do not provide sufficient purchase to permanently hold the screw.
Besides, hook and rod devices, as well as screw and rod devices, generally produce a rigid connection between the rod and each vertebra and, thus, between the vertebrae to be held. However, in some cases it is desirable to allow a controlled relative movement between these vertebrae.
Another kind of known device is disclosed in WO 2009/047352. It comprises a rod, a blocking body surrounding the rod and a ligature. When using such a device, the ligature is passed around a bone and through the blocking body, and the rod is loaded into the blocking body. The ends of the ligature are pulled so as to apply tension to the ligature, the ligature and the rod being simultaneously fastened to the blocking body by means of a fastening system comprising a screw or a nut. Portion(s) of the elongated member are clamped between outer face(s) of the rod and inner face(s) of the blocking body. However, this device does not give complete satisfaction because it may be difficult to handle and/or to operate, especially during the fastening step. Moreover, the manufacturing of this device may be expensive, especially due to the large number of parts that make up the device. Finally, this device takes up much space, especially due to the blocking body which surrounds the rod.